The present invention relates to a condenser microphone having resistance against high temperatures and radioactive rays, which is highly sensitive and which exhibits good frequency characteristics at high temperatures and in the presence of intense radioactive rays.
Microphones are used not only in the audio world but also in industrial fields as sensors in order to convert vibration into electric signals. Many of them are used at ordinary temperature. However, microphones of the piezo-electric ceramic type are used at high temperatures, for example, in a high-temperature coolant (liquid sodium heated to about 700.degree. C.) placed under intense radioactive rays (10.sup.7 R) in a nuclear reactor.
The microphone of the piezo-electric ceramic type, however, has a sensitivity of as low as -105 to -120 dB under the conditions of a high-temperature atmosphere. Therefore, the microphone of the piezo-electric ceramic type is not capable of detecting sound of small levels when it is used in a high-temperature atmosphere condition. Microphones of other types are not utilizable at high temperatures as a matter of course. Therefore, the conventional microphones are not capable of detecting sound of small levels when they are used as sensors under high-temperature atmosphere conditions.